1. Field of the Invention
The present invention relates to a temperature sensor for high temperature which has superior characteristics for heat resistance and a method of producing the same, and more particularly to the material of the thermistor layer.
2. Description of the Related Art
Temperature sensors for high temperature, which employ thermistors, are widely used in various industrial fields. For example, such temperature sensors are applied to temperature sensor for controlling gas combustion or exhaust temperature sensors for automobiles, etc.
These temperature sensors for high temperature are composed of a thermistor layer, electrodes connected to the thermistor layer, an insulator portion which protects these components, and the other components. In a conventional type of such temperature sensors for high temperature, in case that the bulk type thermistor layer is employed, the thermistor layer is made by solidifying powdered chromium oxide or aluminum oxide material (Japanese examined Patent Publication No. 56-23281).
In addition, as a conventional type of thick filmed type thermistor layer, a composition composed of powdered oxides of manganese, cobalt, nickel, iron, aluminum, and silicon, powdered glass and rhodium dioxide (RhO.sub.2) are made into a paste and printed with the electrodes onto a ceramic plate employed as the insulator, then baked (Japanese unexamined Patent Publication No. 54-118599).
Additionally, a ceramic plate using alumina is generally employed as the above insulator.
However, as the thermistor layer containing the above composition reacts violently with alumina at high temperatures and undergoes interdiffusion, the resistance-temperature characteristics of the thermistor layer are made unstable. It is therefore difficult to seal and incorporate the thermistor layer between the ceramic plates.
Meanwhile, in case that the thermistor layer is bared, as it is directly exposed to the combustion flames or the like, the thermistor layer is deteriorated and the bonds between the thermistor layer and the electrodes are also badly influenced.